Re: [Boost-users] [intrusive_ptr] Counting implementation

From: Alan M. Carroll (amc_at_[hidden])
Date: 2008-07-31 08:18:45

At 04:57 PM 7/30/2008, you wrote:
>Compared to mine, better sides:
>Worse sides:
>1. No thread safety (may be you do not need it, but i need).
>2. No const awareness, i think the following will fail:
>  boost::intrusive_ptr<const test> p(new test);
>  boost::intrusive_ptr<const test> q(new test);
>  p = q;
>3.m_reference_count is visible to derived classes. 

1) Yes, but as you note it's trivial to add if it's important. I had that in my own implementation of intrusive_ptr (before those were in Boost) but dropped it because I never used it. Not such a big deal on Win32, but I remember it being painful on Sun / Sparc systems (am I dating myself?).

2) Interesting. I have been using this code for years and not had that come up. I'll have to take a look.

3) A design feature for me. It makes copy on write semantics easier to implement. You might consider putting in "bool is_shared()  const { return m_reference_counter > 1; }" for that case.